Field of the Invention
The invention relates to a process for receiving data and a configuration for conducting the process. The concept "data" also refers to speech data within the scope of this application.
The transmission channels are time-variant and frequency-selective in many information transmission systems, especially mobile radio systems. The procedure is commonly as described below in information transmission systems with time-variant and frequency-selective transmission channels.
Estimation of the transmission properties of the transmission channels is usually done by evaluating and estimating the channel pulse responses (channel evaluation/estimation), which is usually understood to be evaluation/estimation of the amount and phase of the channel pulse responses of the transmission channels. However, detection types are also known which utilize only the amount of the channel pulse responses for determining the transmission properties.
Adaptation of the receiver to the current (estimated) transmission properties or channel pulse responses, whereby it is advantageous to insert knowledge about the transmission properties of the transmission channels in data detection is performed.
Although usually only one current channel pulse response results for a communication connection and the accompanying transmission channel, the discussion in the present specifications is always of an estimation of several channel pulse responses, since new detection processes exist which evaluate the channel pulse responses of several communication connections and the associated transmission channels and utilize them advantageously for data detection. Transmission processes also exist in which a communication connection of several different transmission channels is simultaneously assigned. Other concepts used in connection with the channel pulse response are also introduced in most cases. However, the present application also includes detection techniques in which only one current channel pulse response is evaluated and/or estimated.
In processes known to date, estimations of channel pulse responses are conducted in a certain fixed time frame or even continuously. The receiver is adjusted to the current channel pulse responses after every estimation of the channel pulse responses, i.e., its knowledge about the transmission properties of the transmission channel is updated, so that it can advantageously be inserted in data detection.
The adjustment of the receiver to the current channel pulse responses takes place differently according to the information transmission system. This is presented briefly below by way of several examples.
Channel pulses are used in the GSM for adjustment of multipliers in the criterion formation of the Viterbi detector.
In direct sequence (DS) CDMA mobile radio systems such as, for example, the IS-95, a rake receiver is usually inserted for data detection. Adjustment of the receiver to the current channel pulse responses thereby takes place by setting or adjusting the rake fingers.
In a wideband TDMA system (e.g., a band width of about 2 MHz) with a decision feedback equalizer (DFE), channel pulse responses are used to calculate the filter coefficients of the forward or backward feed filter. An equation system must be solved at great expense to calculate the filter coefficients of the DFE. This is also the case for a wideband TDMA system with a DFSE. The decision feedback sequence equalizer (DFSE) is a combination of MLSE and DFE.
Several different process steps are conducted for data detection in the receiver of a JD-CDMA system. Adjustment of the receiver to the current estimated channel pulse responses essentially takes place, for example with the use of the zero forcing block equalizer (ZF-BLE), essentially in the following 4 steps.
Step 1: For all participants k=1, . . . ,K, folding of channel pulse response h.sup.(k) of participant k with participant-specific CDMA code c.sup.(k), whereby the result is combined pulse response b.sup.(k). There can also be several channel pulse responses per participant.
Step 2: Determination of system matrix A based on the combined pulse responses b.sup.(k) of all K participants, k=1, . . . ,K.
Step 3: Determination of the matrix A.sup.H A (the H set above symbolizes the operation "conjugated complex transposed").
Step 4: Calculation of the Cholesky breakdown of A.sup.H A.
Adjustment of the receiver to the current channel pulse response in all cases presented above as examples requires considerable expense, since the performing of many operations such as multiplication, addition, and data transfer to execute the adjustment requires considerable computer work and therefore also high current consumption.
The task presented for the invention is consequently to provide a process and a configuration for conducting the process with which it is possible to achieve reception of data with as low an expense and as high a quality as possible.
As was mentioned above, the estimations of the channel pulse responses are measured in processes known to date in a certain fixed time frame or are even measured continuously. The receiver is adjusted to the current channel pulse responses after every estimation (evaluation). This adjustment accordingly usually also takes place in a fixed time frame. For example, GSM and JD-CDMA use training sequences with which the pulse responses of the mobile radio channels are estimated. These training sequences are measured for each transferred burst, and the receiver is then adjusted to the current channel pulse responses. So-called pilot signals are used in conventional direct sequence (DS)-CDMA mobile radio systems, for example IS-95, to determine the channel properties of the mobile radio channel. These pilot signals are even sent out continuously.
In the case of expensive simulations with simulation instruments expressly manufactured for this purpose, however, it was found that under certain conditions in information transmission systems it could happen that the transmission properties of the transmission channels and accordingly the channel pulse responses altered more slowly than according to the above mentioned fixed time frame. Therefore, the transmission properties of the transmission channels and accordingly the channel pulse responses change so slowly or so insignificantly that it is not necessary to make an adjustment of the receiver to the actual channel pulse values after each evaluation of the channel pulse responses, which indeed take place according to a given fixed time frame. This situation occurs to a greater extent in TDMA systems and accordingly also in JD-CDMA and GSM systems if several consecutively following time slots of the TDMA frame are assigned to one participant. The adjustment of the receiver to the current channel pulse response in a fixed previously determined time frame in this case represents an unnecessary expense that improves data detection only slightly.